Authentication of milk thistle commercial products using UHPLC-QTOF-ESI+MS metabolomics and DNA metabarcoding

Milk thistle is one of the most popular hepatoprotectants, and is often sold in combination with other ingredients. Botanical supplements are known to be vulnerable to contamination and adulteration, and emerging technologies show promise to improve their quality control. Untargeted and semi-targeted metabolomics based on UHPLC-QTOF-ESI+MS techniques and DNA metabarcoding using Illumina MiSeq were used to authenticate eighteen milk thistle botanical preparations (teas, capsules, tablets, emulsion). Untargeted metabolomics separated 217 molecules and using multivariate analysis discrimination of the different groups was established. Semi-targeted metabolomics focused on 62 phytochemicals, mainly silymarin flavolignans that act as putative biomarkers of authenticity. All formulations contained molecules from silymarin complexes at different levels. The quantitative evaluation of silybins was done using in parallel UV spectrometry and UHPLC-QTOF-ESI+MS and their correlations were compared. DNA metabarcoding detected milk thistle in eleven out of sixteen retained preparations, whereas two others had incomplete evidence of milk thistle despite metabolomics validating its presence. Metabolomics enabled the identification and quantification of marker compounds in the samples, while DNA metabarcoding provided insights into the total species composition allowing the interpretation of the results in a broad context. Our study emphasizes that combining spectroscopic, chromatographic, and genetic techniques brings complementary information to guarantee the quality of the botanical formulations.